Many medical tests, including pap smears, require a physician to collect cells by brushing and/or scraping a skin or mucous membrane in a target area with an instrument. The cells are then smeared onto a slide, and are fixed and transported to a laboratory where the slide is stained. The slide can then be examined under a microscope by a cytotechnologist and/or a pathologist to identify cellular abnormalities. During evaluation, a pathologist may employ a polychrome technique, characterized by staining the nuclear part of the cells, to determine the presence of dysplasia or neoplasia. The pathologist may also apply a counter-stain for viewing the cytoplasm of the cells. Because the sample may contain debris, blood, mucus, and other obscuring artifacts, the test may be difficult to evaluate, and may not provide an accurate diagnostic assessment of the collected sample.
Cytology based on the collection of the exfoliated cells into a liquid preservative offers many advantages over the traditional method of smearing the cells directly onto the slide. A slide can be prepared from the cell suspension using a filter transfer technique, as disclosed in U.S. Pat. Nos. 6,572,824, 6,318,190, 5,772,818, 5,364,597, and 5,143,627, which are expressly incorporated herein by reference.
Filter transfer methods generally start with a collection of cells suspended in a liquid. These cells may be collected and dispersed into a liquid preservative or they may naturally exist in a collected biological liquid. Dispersion in liquid preservatives containing methanol, such as PreservCyt™ solution, breaks up mucus and lyses red blood cells and inflammatory cells, without affecting the cells of interest. The liquid is then passed through a filter with a fixed diameter aperture covered by a membrane to concentrate and collect the cells. Debris, such as lysed blood cells and dispersed mucus, which flow through the pores of the membrane, are not collected on the membrane and are greatly reduced by the combined method of dispersion and filtering. Then the cells collected on the membrane are transferred onto a slide.
Existing filter transfer methods use filters with a fixed diameter aperture. Therefore cell samples spots are of a uniform size, i.e., 21 mm, even when smaller spots, i.e., 7 mm, are desired for a specific test. A prior device for collecting a dispersed monolayer of cells, and for transferring them to a microscope slide for examination, has a tube with a filter-positioning rim with a highly planar geometry to position a filter for transferring collected cells to the microscope slide with faithful retention of the spatial distribution of the collected particles. The equipment for manufacturing and using this device is standardized based on the diameter of the tube on which the filter is fixed.
It has been found that adjusting the aperture of this known filter device of the type described above without changing the diameter of the tube leads to microfluid dynamic effects that distort the spatial distribution of the collected particles upon transfer. Methods of adjusting the aperture include the use of a Mylar® ring on the underside of the filter and use of a membrane with open and closed areas.
Consequently, existing filter transfer methods use filters with uniform apertures and may result in excess cells being transferred and subsequently discarded. These excess cells require the use of extra test reagents, leading to increased costs. Reducing the amount of cells lost while forming a cell sample not only reduces the amount of test reagent used, but also increases the number of tests that can be performed on cells retrieved during one sample collection procedure. This in turn allows for more confirmation testing, conserves difficult to collect cells, and reduces the number times a patient would be subjected to a collection procedure.
Accordingly, there exists a need for a device and method for forming samples of varying specific sizes using filter transfer methods. There also exists a need for a device and method for forming samples of varying specific sizes while maintaining a standard tube size and faithful retention of the spatial distribution of the collected particles.